Solid ink or phase change ink printers conventionally receive ink in a solid form, sometimes known as solid ink sticks. The solid ink sticks are typically inserted through an insertion opening of an ink loader for the printer, and are moved by a feed mechanism and/or gravity toward a heater plate. The heater plate melts the solid ink impinging on the plate into a liquid that is delivered to a melt reservoir. The melt reservoir maintains the ink in a melted state and delivers the ink to a printing system of the printer for ejection onto an image receiving surface. The image receiving surface can be the surface of media, such as paper, or a liquid layer of release agent supported by an intermediate imaging member, such as a metal drum or belt.
Currently, efforts are underway to use phase change inks in magnetic character ink recognition (MICR) printing. MICR printing uses aqueous magnetic inks to print characters on financial documents to enable character recognition technology that detects the characters with magnetic detectors. This technology is used primarily in the banking industry to facilitate the processing of checks. The technology allows magnetic readers to read information, such as routing numbers and account numbers, from printed documents. Unlike barcodes or similar technologies, however, MICR codes can also be easily read by humans.
MICR printing ink typically includes a suspension of metal particles, such as iron oxide, which enable the magnetic readers to recognize the printed characters. In MICR solid ink, the metal particles are suspended in a phase change medium. When MICR solid ink is melted and in a liquid state, the metal particles can be pulled downwardly by gravity and collect in the lower regions of melted ink containers and passageways in a printer. The metal particles settling out of the ink can degrade the uniform distribution of magnetic particles in the ink that can make characters printed with the non-uniform ink difficult to detect.
Uniform distribution of metal particles in phase change ink is more difficult than maintaining such distribution in aqueous inks because the viscosity of the phase change ink and the ability of the ink to change phase affects the flow dynamics of the ink. Consequently, previously known methods of maintaining a uniform distribution of metal particles in aqueous inks are not as effective or robust with phase change inks. Thus, a need exists for devices and methods that help maintain a uniform distribution of metal particles in phase change ink as the ink is used in an inkjet printer.